摘要：举例液压系统空穴导致的液压泵低压灯灯亮事件，分析放气原理和提出放气操作建议。

液压系统有空气除了会使液压部件作动异响外，还会导致液压泵低压灯亮。我们曾遇到过三次。

2013/02/08  737-800飞机

起飞收起落架时，A系统EDP和EMDP低压灯亮约2秒，系统压力正常，后面航段都正常。查询前一天航后更换了左发EDP供油管。

2015/11/23  737-800飞机

起飞离地大约200英尺后，左发EDP和EMDP低压灯同时亮，大约持续3秒，后续飞行时间正常。查询为更换左发后执行的首班。

  2017/12/23   737-800飞机

起飞收起落架时，A系统EDP和EMDP低压灯亮，起落架无法收起，约十秒后两个低压灯熄灭，起落架收起。查询前日航后更换了左发EDP。

刹车管路放气原理图

1. 设置停留刹车；

2. 操纵副翼和扰流板全行程10次；

3. 收放相应反推5次；

4. 将飞机恢复至正常。

a.全行程作动副翼、升降舵、方向舵各三次。

b.收放襟缝翼三次。

c.收放反推。

d.从UP到DN位作动起落架手柄三次（作动前确认起落架安全销已插好）。

e.全行程作动水平安定面至少三次，确保感觉压差灯不亮。

a.如果更换的部件在正常刹车系统防滞活门上游，按AMM32-41-00-710-001放气。

b.如果更换的部件在正常刹车系统防滞活门下游，按AMM32-41-00-710-001和AMM32-41-00-710-002放气。。

c.如果更换的部件在备用刹车系统防滞活门上游，按AMM32-41-00-710-003放气。

d.如果更换的部件在备用刹车系统防滞活门下游，按AMM32-41-00-710-003和AMM32-41-00-710-004放气。

Description

On 5-Apr-13,polit reported two "low pressure" lights of GUN039 hydraulic system A were on for about 2 seconds when retracting landing gears at the first leg,and the fault did not return in the following legs.GUN checked hydraulic reservoir pressurization system was normal,and records show that hydraulic system A EDP supply line(PN：155106-20-11) was replaced on 4-Apr-13 post-flight.

On 8-Feb-13, similar symptom was occurred on GUN039: two "low pressure" lights were on after replaced hydraulic system A EDP supply line at the first leg.

But "low pressure" lights did not on after replaced hydraulic system A EDP supply line at the first leg for other airplanes.

Desired Action

1) Has Boeing received reports from other 737NG operators with similar reports as reported above?

2) If yes, what suggestions did Boeing give to resolve this issue?

3)Would you please provid procedure for EDP supply line Installation Test?

RESPONSE:

1.  We have not received any reports identical to GUN's.  However, we have received occasional reports of odd system behavior due to air trapped in the system due to maintenance.

2. and 3.  We believe that GUN's incidents are due to air in the EDP supply line; as the pump is run, the air causes a momentary low pressure, until normal system operation eventually pushes the air on into the reservoir.  To resolve this, GUN may wish to try the following procedure after replacing the EDP supply line:

1.  Set the parking brake.

2.  Run the engine associated with the affected system.

3.  Turn off the electric motor-driven pump on the affected system.

4.  Turn the control wheel full left, then full right, so that ailerons and flight spoilers move.  Repeat ten times.

5.  Return the airplane to normal.